Recently, a method of performing diagnosis has attracted attention, in which indocyanine green (ICG) is administrated into a body as an optical contrast agent, the ICG is excited by irradiating excitation light, or the like, a fluorescence image of near infrared emitted by the ICG is imaged with a subject image, and the image is observed.
Regarding the method, an imaging device including an aperture diaphragm, which images a fluorescence observed image emitted from an observed part of a subject by irradiating excitation light, with an subject image by the irradiating light, has been known (refer to PTL 1).